When you upload an image from your computer to a post on WordPress, you get an option to select the size via either Thumbnail, Medium or Large. This allows us to resize the images appropriately as WordPress picks the appropriate image size based on the theme in use. However, the same is not available when you insert and image using Press It bookmarklet. The three size selection option (thumbnail, medium, large) is not available in the editor because the image is already inserted by the bookmarklet.
Hope WordPress looks into this inconvenience.